In the case of an acoustic piano, when a damper pedal is stepped down, a damper felt gets away from each string according to rotation of a damper lever in all keys. When an optional key is pressed in this state, an action comes into operation responding pressing of the key, a hammer strikes a string, vibration of the string is transferred to a sound board, a music sound is emitted, and resonance (damper resonance) comes to be generated between all other strings. It is configured that the damper felt is in contact with the string and suppresses vibration at the normal time (when the damper pedal is not stepped down).
In the case of an electronic piano, it is conducted to improve reality of the sound by providing various additional sounds and additional effects other than the actual sound of the piano which becomes main, and to make the sound similar to the emitted sound of an acoustic piano.
In order to reproduce the damper resonance described above, in an electronic piano of a related art, a process of providing an effect of resonance to a sound source at the time a music sound was emitted (stereo output process of the damper resonance) was conducted.
In a stereo output process of the damper resonance, a signal outputted eventually was created by providing left and right sound volume for localization with respect to plural resonance sounds and synthesizing the output of the positive phase and the reverse phase.
Also, in Japanese Patent No. 3061403, there is disclosed a technology for providing an echo after localization with respect to the sound of a pipe organ in an electronic musical instrument imitating the sound of a pipe organ.